Communications networks such as optical networks often employ wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to increase transmission capacity. In WDM and DWDM networks, a number of optical channels are carried in a single fiber at disparate wavelengths. Network capacity is based on the number of wavelengths, or channels, in each fiber and the bandwidth, or size of the channels. In WDM, DWDM and other optical networks, arrayed waveguide gratings (AWGs), interleavers, and/or fiber gratings (FGs) can be used to add and drop traffic at network nodes and to multiplex and demultiplex traffic at network nodes. To enable reconfiguring the wavelength paths to be dropped or added at different nodes, network nodes having optical switches can be provided, known as all optical ROADM (Reconfigurable Optical Add Drop Multiplexer) nodes.
DWDM networks typically use more network elements than earlier point to point optical links, for example—optical amplifiers, multiplexers, demultiplexers, and dispersion compensation units, which can bring reliability concerns and warrant monitoring. Thus there was a need for transmitting overhead information for management and for protection schemes to recover from equipment failures. As a result, the G.709 Optical Transport Network, or OTN standard was generated by the International Telecommunication Union Telecommunication Standardization (ITU-T) to provide management functionality for DWDM optical networks. OTN involves adding a frame of overhead information, (also called a digital wrapper), some to the front of the signal as a header, and some such as FEC (Forward Error Correction) as a trailer appended to the rear. The FEC can extend optical span distances by reducing bit error rates (BERs).
The G.709 standard framing involves amongst others an ODU overhead, as well as an OTU overhead.
The OTN hierarchy, based on ITU-T G.709, has just evolved in order to cope with the present and future requirements in terms of new CBR and packet clients to be transported in the optical backbones of the telecom operators. In order to avoid the proliferation of new ODUk containers, specified to transport possible future clients, and in order to build a “future proof” OTN Network ITU-T (in particular SG15 Q11) has defined a new type of ODU container: the ODUflex. The ODUflex has been included in the last revision of G.709.
The ODUflex has the following main characteristics:                The OPUflex/ODUflex frame structure is the same as the one already defined for the other ODUk (k=0, 1, 2, 3, 4);        Any new CBR clients 1.238 G will be mapped into ODU0. Clients>1.238 G and less than or equal to 2.488320 G will be mapped into ODU1.        CBR clients, supra-2.488 Gbit/s (with bit rate tolerances up to ±100 ppm)—except CBR2G5, CBR10G and CBR40G, whose mapping is already defined in ODU1, ODU2 and ODU3—will be mapped into ODUflex via bit-synchronous mapping (BMP);        New “packet” clients or VLAN will be mapped into ODUflex via GFP-F;        ODUflex signals have to be transported through the optical network over an HO-ODUk (i.e. ODU2, ODU3 and ODU4) signals and then via the relevant OTUk through the Line. The ODUflex is mapped into the HO-OPUk using GMP (i.e. Generic Mapping Procedure).Furthermore ITU-T has defined a resizing protocol to improve the ODUflex flexibility. This protocol is defined in the G.Hao/G.7044 recommendation. As per LCAS in SDH, this protocol will allow resizing of the dimension of the ODUflex when the quantity of the traffic to be transported increases or decreases during the “life” of the ODUflex.        
At the moment the most interesting application for the ODUflex seems to be the transport of selected stream of packets inside the optical network. For instance the traffic associated with a particular customer/application, identified by a particular VLAN, can be mapped inside a specific ODUflex. From that moment, that traffic can be independently routed inside an Optical transport network designed according to G.798 (i.e. a network made by DWDM equipments and ODUk cross-connects, where the ODUk cross-connects are able to switch ODUflex) without the need to go down to packet level every time that traffic has to be re-routed.